1.The neutralizing antibody titer of recovered ducklings started to raise gradually from the 7th day postinfection, and reached the titer of log 1.25 to 4. 75 at the 14th day.It stayed at the level of log 2.5 to 5.0 30 days later and lasted till 120 days. The sera collected from 60-day一oldslaughtered ducks had the titer of log 3.25-5.0, and could be used for emergency control of the disease.
2. About 20 ml of antiserum could be collected from each slaughtered duck.
3. The ducklings inoculated passively with recovered ducks'sera (with VN antibody le,·el over log 3.0) could rapidly possess antibody and keep it for 14~20 days.
4. In six uncontaminated farms, 11, 110 susceptible ducklings were inoculated with sera from recovered ducks and 2,880 ducklings served as uninoculated controls. The mortality of the control group (4.41%) was ten folds higher than that of inoculated group (0.38%).
5.In five DHV-contaminated farms, the mortality of 4,700 inoculated ducklings was only 0. I一1.9%(0.91% in average), while that of 1,770 uninoculated controls was 8.6一60%, The mortality of the inoculated gro??p was much lower (20 times) than that of uninoculated control.
6.Ducklings (2,087,979 in total)raised both in Kaohsiung and Han prefectures were inoculated with the spcific antisern since September 1971-December 1972,Among them,13,303 heads were a<l and the mortality was 0.63%.